MySQL Trigger: Delete From Table AFTER DELETE

Question

Scope: Two tables. When a new patron is created, they have some information about them stored into a 2nd table (This was done using a trigger as well, it works as expected). Here's an example of my table structure and relationship.

Table 1-> patrons

+-----+---------+-----+
+  id +   name  + val +
+=====+=========+=====+
+  37 +  george +  x  +
+-----+---------+-----+
+  38 +  sally  +  y  +
+-----+---------+-----+

Table 2 -> patron_info

+----+-----+----------+
+ id + pid +   name   +
+----+-----+----------+
+  1 +  37 +  george  +
+----+-----+----------+
+  2 +  38 +  sally   +
+----+-----+----------+

The administrator can manage the patrons. When they choose to remove a patron, the patron is removed from the table 1 patrons. At this point, nothing happens to table 2 patron_info.

I'm simply trying to create a trigger to delete from table 2, when table 1 has an item deleted. Here's what I've tried...

Initially, I try to drop the trigger if it exists (just to clear the air)...

DROP TRIGGER IF EXISTS log_patron_delete;

Then I try to create the trigger afterwards...

CREATE TRIGGER log_patron_delete AFTER DELETE on patrons
FOR EACH ROW
BEGIN
DELETE FROM patron_info
    WHERE patron_info.pid = patrons.id
END

At this point, I get a syntax error 1046: Check syntax near END on line 6. I don't know what the error is at this point. I've tried several different variations. Also, am I required to use a delimiter here?

Can anyone help restore my sanity?

Solution 1

I think there is an error in the trigger code. As you want to delete all rows with the deleted patron ID, you have to use old.id (Otherwise it would delete other IDs)

Try this as the new trigger:

CREATE TRIGGER log_patron_delete AFTER DELETE on patrons
FOR EACH ROW
BEGIN
DELETE FROM patron_info
    WHERE patron_info.pid = old.id;
END

Dont forget the ";" on the delete query. Also if you are entering the TRIGGER code in the console window, make use of the delimiters also.

Solution 2

Why not set ON CASCADE DELETE on Foreign Key patron_info.pid?

Comments

[vivek_jonam]

What help would you need here? what is your real question?

[Ohgodwhy]

@vivek_jonam The delete trigger won't fire. It gives me a sytnax error on 'END' at line 6. Also, do I wrap this in a DELIMETER $$?

[zerkms]

@Ohgodwhy: just a note about memcache question - it was linked only after I added it. It was no in "Related" before I did it.

[Ohgodwhy]

Maaaaaaaaaaaaaaaaaan. It all ended up being the semicolon in my WHERE clause. I'm such a fool. Thanks for that vivek, it's appreciated!

[Air]

Why use a compound statement block for just one statement? There's no requirement in the CREATE TRIGGER syntax to do so.

[Ulterior]

dont forget the ";" - should be in BOLD

[muffir]

If the table engine supports foreign keys this solution should be prefered before using trigger to do that.